In tropical architecture one of the most important elements of a building is its roof. In the region which is characterized with strong sun radiation and high rainfall, the roof is essential element that makes a house a shelter. When the Europeans reached the tropical countries and settled in various places of these regions during the colonial expansion period, they built themselves houses that purportedly designed to be climate responsive. In order to anticipate the sweltering heat and torrential tropical rain, their houses were built with big sloppy roof with wide eave that is commonly known as the hip roof. Not only that, the colonial houses typically have a high ceiling and lot of ventilation openings to make sure that the warm air does not get trapped inside the space. These houses also typically have a verandah where people would sit to catch a breeze.
Fast forward, gone are those days where people live in close interaction with their surroundings. While houses with ample openings, high ceiling and minimal air-conditioned space are still highly favored, such ideal houses are often out of reach for many and are considered a luxury. With the rapid urbanization and densification that happens along the way, people are living in many cases cheeks to jowls with their neighbors. Soaring land price means for many people having to live on a small plot of land an everyday reality. For many people, lots of ventilation opening means loss of privacy and a compromise of safety. The degradation of environment quality especially in urban areas (due to eg. air pollution, noise pollution) also makes most people avoid unnecessary exposure with the outdoor. Thus people live in their own cells, shut from the outside world where constant need of coolness is fed by air-conditioners. The changing of environment quality and crowded living condition have created a peculiar type of architecture where buildings are designed to be able to be sealed completely and air-conditioned.
With the decreasing of passive ventilation system, height of ceilings and increasing needs of air-conditioners in most modern homes, roof installation plays a crucial role in creating home comfort and achieving energy efficiency. However more often than not, homeowners leave its selection to the designers or contractors while focusing to deal with the aesthetic appearance of the more visible parts of the projects.
There are few popular types of roof insulation system for pitched roof which is differentiated by application techniques. They are, to name among others: reflective system, blanket or rolls insulation, loose-fills insulation, blow in insulation, foam board system, spray-foam system. Aluminum foil and bubble foil is one of the most known reflective type of insulation. Rockwool and glasswool are materials that can be applied as loose fills or blanket insulation. Cellulose is one type of blow in insulation material. Extended polystryrene or EPS and polyurethane are two common foam board insulation materials. Polyurethane can also be applied as a spray-foam material, this kind of material is said to be the most effective and a more green option.
In Southeast Asia, the reflective system i.e. aluminum foil and bubble foil and blanket insulation i.e. rockwool are popular. In Indonesia, aluminum foil is the most common choice for residential projects. Please note however that aluminum foil for roof insulation comes in many variety of thickness and different layering such as to name among others a single layer woven or non-woven foil, double layer foil with a foam sheet sandwiched in the between or single foil with foam backing. Bubble foil which is often considered as a type of aluminum foil too, is also used though not very common. Bubble foil provides a more efficient heat insulation. Due to its higher cost however it is mainly used in higher budgeted buildings. Most housing projects use foam backed aluminum foil while a budget conscious home owners would use the woven aluminum foil. Low cost housing on the other hand often forgoes the roof installation at all.
Glasswool (instead of the denser rockwool) are commonly used for Indonesian factories which mostly use them also because of its ability to insulate noise. Some architects however would recommend rockwool for their housing projects too when the clients can afford it.
For tropical context, using aluminum foil of thinner variety as standalone roof insulation however does not really offer an efficient heat insulation. Despite of many claims made by various suppliers about the efficiency of such aluminum foil in reducing heat, many experience builders would say that R-value(thermal resistance value) of heat insulation materials goes hand in hand with thickness of insulation materials and that consumers should do their homework before taking such statements at a face value.
This kind of aluminum foil is commonly used as sarking, which basically acts as radiant barrier (reflect the sun heat) and acts as vapor barrier. Aluminum foil is ideally used together with rockwool or bubble foil to reduce heat more substantially. This is not unlike roof insulation system that is commonly installed in the temperate climates where the different between indoor and outdoor temperature is great.
In the tropical area, rockwool is particularly ideal as roof insulation for air-conditioned space and it works hand in hand with the aluminum foil which acts as the vapor barrier on the warm air side. Without the aluminum foil, the warm and humid air will come in contact with cool air-conditioned surface would create condensation which in the long term can affect the integrity of roof structure. In case of timber structure, it will eventually rot. In the case of metal structure, it will lead to corrosion.
Using the two types of roof insulation namely the reflective system (i.e.aluminum foil) and the loose-fill or blanket system or bulk insulation system as some might call it (i.e. rockwool) would give other benefits beyond heat insulation. It would provide condensation control, noise insulation and also help to reduce energy consumption. However cost of opting to use this ‘double treatment’ remains an obstacle for many budget conscious homeowners. In such case, it is worth to point out that many homeowners in the hot climate region would argue that an adequate attic space equipped with attic vents or turbine vents will naturally act as reliable heat insulation.
By: Devisanthi Tunas